Truckers and motor vehicle operators have in the past maneuvered their vehicles into loading docks utilizing visual cues, mostly through the utilization of side mirrors or in some cases remote-controlled cameras. Mostly the backing of a vehicle is performed safely only with a skilled operator. It will however be appreciated, especially with trailers and other large vans, that there is a large blind spot to the rear of the vehicle, which prevents the operator from visually assessing the distance to either a loading dock or to alert him to the passage of an individual, animal or child behind the vehicle.
In another field, verbalization of depth through the utilization of annunciating depth sounders includes U.S. Pat. Nos. 4,489,405, 4,621,348, 4,616,350, 4,672,590 and U.S. Pat. No. 4,234,941 which, inter alia, describe the verbal annunciation of the depth of water under a marine vessel. The transducers utilized in such situations are not applicable to through-the-air transmission and therefore sonic ranging for land based vehicles is not contemplated with the sonar systems utilized for aquatic navigation.
Moreover, while through-the-air acoustic ranging has been achieved through the utilization of transducers produced by the Polaroid Corporation, they have proved to be unsuitable for use in vehicular applications primarily because the particular through-the-air transducers are deleteriously affected by hydrocarbons, road grime and dirt. Moreover, the beam width of such transducers is excessively narrow which makes it difficult if not impossible to provide for the type of coverage which would prevent the backing of a vehicle into a pedestrian, animal or unseen structural impediment. The problem with the Polaroid-based technology is so severe that even when contemplating utilizing such sonar systems for automotive speed control or braking control so as to prevent vehicular accidents, such systems have universally been rejected due to the problem of providing a suitable transducer.
By way of further background, sonar ranging through the air has been utilized in industrial process environments in which the position of articles on a conveyer belt is monitored through a short-distance sonar ranging system. It will be appreciated however that these systems can be controlled as to the environment and therefore the transducers utilized can be operated in a clean environment in order to assure production line operation. Typically, these systems do not operate for ranges in excess of tens of feet, and therefore are not suitable for vehicular use. Moreover, safety factors are not as severe in the industrial environment, and safeguards for maintaining production are relatively easy to achieve in such a controlled environment.